Field of the Invention
The present invention relates to a mirror drive device equipped with a mechanism for high-speed driving of a mirror unit provided in an image pickup apparatus, such as a single-lens reflex camera, and an image pickup apparatus equipped with the mirror drive device.
Description of the Related Art
In a mirror drive device mounted on an image pickup apparatus, such as a single-lens reflex camera, an operation for retracting a mirror unit formed by a main mirror and a sub mirror from a photographing optical path during photographing and an operation for moving the mirror unit into the photographing optical path during finder observation are performed at high speed. Each mirror of the mirror unit having entered the photographing optical path is brought into contact with an associated stopper formed on the mirror drive device, thereby being positioned in a predetermined stop position to guide an object light flux having passed through a photographic optical system to a viewfinder optical system and a focus detection unit.
As such a mirror drive device as described above, there has been proposed one equipped with a direct drive mechanism for directly driving the main mirror. In this proposed mirror drive device, a voice coil motor causes the main mirror to move from a mirror-down position where the main mirror is in the photographing optical path to a mirror-up position where the main mirror is retracted from the photographing optical path. Further, the main mirror is engaged and locked in the mirror-down position using a locking lug which is slidably moved by a solenoid, and the main mirror is released from the locked state by energizing the solenoid to drive the same slidably moving the locking lug (see Japanese Patent. Laid-Open Publication No. 2010-44271).
In a quick return mechanism. e.g. of a single-lens reflex camera, the mirror unit is rotated between the mirror-down position and the mirror-up position by rotating the main mirror with a spring force, and causing the sub mirror to follow the main mirror using a toggle spring and an inversion cam.
However, in the mechanism that drives the mirror unit using the spring force, to rotate the mirror at high speed, it is necessary to use a spring having a large spring force. For this reason, a large torque is required to charge the spring at high speed during rotation of the mirror, which requires an actuator having a large driving force, or a reduction gear having a large reduction ratio.
To solve this problem, conventionally, there has been proposed a mirror drive device using a spring member which inverts its urging direction during rotation of a mirror (see Japanese Patent Laid-Open Publication No, 2006-30498). In the proposed mirror drive device, the spring member applies the urging force to the mirror in a direction in which the mirror is retracted, when the mirror is in a position for finder observation, and applies the urging force to the mirror in a direction toward the position for finder observation, when the mirror is in the retracted position.
However, in the mirror drive device proposed in Japanese Patent Laid-Open Publication No. 2010-44271, the solenoid which is an additional driving source is required to release the main mirror from the state locked using the locking lug. This increases not only the power consumption, but also manufacturing costs, and further, a space for arranging a slide mechanism for the locking lug and the solenoid is also required, which increases the size of the mirror drive device, leading to an increase in the size of the camera.
Further, in Japanese Patent Laid-Open Publication. No. 2006-30498, after the mirror reaches a position where the urging direction of the spring member for applying the urging force is inverted during rotation of the mirror, it is necessary to always charge the spring member. This increases a load in a charging region of the spring member, which limits achievement of lower torque in rotating the mirror.